This project has three parts involving the capacity of three different components of gram negative bacteria to stimulate mitogenesis of murine B cells. The first involved the question f whether the Haemophilus influenzae type b capsular polysaccharide is a murine B cell mitogen as reported in 1986. We found that vaccine quality polysaccharide is not, itself, a B cell mitogen and only research grade polysaccharide containing significant contamination with lipopolysaccharide was mitogenic. The second part of this project was to determine if an H. influenzae type b polysaccharide-meningococcal outer membrane protein conjugate vaccine (Hib- OMP) was a murine B cell mitogen like the outer membrane protein alone which was reported by two labs to be mitogenic. We found that Hib-OMP was, indeed, a mitogen for murine B cells. The above two parts were completed previously. Studies have been completed for part 3, to determine if lipooligosaccharides from human pathogens such as H. influenzae, Neisseria meningitidis and Bordetella pertussis containing short )-site chains, are more potent B cell mitogens than lipopolysaccharides. The results indicate that if the various preparations are compared on an equal molar basis they have similar mitogenic activities, although, the lipooligosaccharide from Neisseria meningitidis was consistently found to be somewhat more stimulatory and exhibited a broader dose response curve. We found there was no correlation between mitogenic capacity and O-side chain length, comparing these lipooligosaccharides to a smooth Escherichia coli lipopolysaccharide. We completed these studies by examining the mitogenic capacity of several Salmonella minnesota mutants having different O-side chain lengths to wild type smooth LPS. Again, no correlation was found between O-side chain length and mitogenic capacity. Manuscripts of these studies are in preparation.